Effect of Insecticides on Various Field Strains of Diamondback Moth and Its Parasitoid in Indonesia

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1 Effect of Insecticides on Various Field Strains of Diamondback Moth and Its Parasitoid in Indonesia Mohammad Iman, Dandi Soekarna, Jestmandt Situmorang¹, I. Made Garus Adiputra², and lshak Manti³ Bogor Research Institute for Food Crops, P 0 Box 368, Bogor 16001, Indonesia, Faculty of Biology, Gadjah Mada University, Yogyakarta, Indonesia, ²Faculty of Agriculture, Department Pests and Diseases, Udayana University, Jalan Sudirman, Denpasar, Indonesia, ³Sukarami Research Institute for Food Crops, P 0 Box 34, Padang, West Sumatra, Indonesia. Abstract The susceptibility of four field strains (Tawangmangu, Pacet, Kopeng and Lembang) of diamondback moth to the synthetic pyrethroids, carbaryl and Bacillus thuringiensis was assessed in the laboratory as well as in the field. Results indicated that there were differences in insect susceptibility depending upon their origin. In general, Lembang and Kopeng strains were more resistant than Pacet and Tawangmangu strains to all insecticides tested except B. thuringiensis. The susceptibility of the diamondback moth parasitoid, Diadegma eucerophaga, from two major cabbage centers (Lembang and Pacet) was also tested. Results indicated that Lembang strain has developed resistance to fenvalerate. The efficacy of B. thuringiensis was lower compared to the synthetic pyrethroids and carbaryl. However, field assessment in West Sumatra indicated that B. thuringiensis applied singly or in combination with synthetic pyrethroids gave significantly higher yields than quinalphos as a standard insecticide. B. thuringiensis was less toxic to D. eucerophaga. Introduction Cruciferous vegetables are economically very important to farmers in the highlands and in specialized production areas of Indonesia. These farmers use input intensive agronomic practices because the sale of these vegetables provides an important source of ready cash income. However, crucifer production in recent years has been seriously affected by a steady increase in the incidence of insect pests. Two major insect pests, diamondback moth (DBM), Plutella xylostella L. (Lepidoptera: Yponomeutidae), and Crocidolomia binotalis Zell (Lepidoptera: Pyralidae) feed on the leaves of cruciferous plants from seedling stage to harvest and greatly reduce both yield and quality of the produce. During the dry season, heavy infestation of DBM can cause 100% yield loss if no insecticides are used (Sudarwohadi 1975). During the wet season, the yield loss still can be 30% (Sudarwohadi and Eveleens 1977). Oka (1976) reported that the yield loss from this insect ranged from 46 to 90%. Insecticides are considered the most effective means of protecting crops against insect damage as they provide rapid control of whole pest complexes of major cruciferous pests. Usually farmers use large quantities of chemicals, often spraying a cocktail of compounds. Woodford et al (1981) reported that the farmers of West Java used about 16 kinds of insecticides to control pests of cruciferous vegetables. The most popular insecticides now are the synthetic pyrethroids fenvalerate, permethrin, and deltamethrin.

2 3 14 Iman, Soekarna, Situmorang, Adiputra, and Manti In North Sumatra, the most popular insecticides are permethrin and chlorpyrifos. As a consequence of frequent insecticide use, DBM has developed resistance to practically all categories of insecticides, and minor insect pests have become major problems in some areas. In 1953, the development of insecticide resistance to DDT was first noted in Lembang by Ankersmit (1953). In the 1960s, organophosphorus insecticides were used intensively in the Lembang area. Since then, resistance to most of the commonly used insecticides has been observed in this insect. In 1977, farmers started to use synthetic pyrethroids such as permethrin and deltamethrin. Permethrin at a rate of 7.5 to 15 g AI/ha could then effectively control DBM at Pujon in East Java and Kabanjahe in North Sumatra (Sitanggang 1977). But in 1982, the DBM population from West Sumatra and West Java could only be controlled when the dosage of permethrin was increased to 40 g AI/ha. Likewise, deltamethrin at a rate of 7.5 to 12.5 g AI/ha could initially control DBM at Margahayu and Segunung, however, since 1982 a dose of at least 30 g Al/ha has been required to control DBM at these locations (Sudarwohadi 1983). These observations suggested that the DBM population is becoming resistant to this new group of compounds. Studies were initiated in 1982 to determine DBM's response to pyrethroids, carbamates, and microbial insecticides. The results reported here represent the data obtained in 1982 and Materials and Methods Two laboratory studies and three field experiments were conducted in 1982 and Laboratory Study I (1982) This experiment was conducted at Segunung, in West Java. Insecticides Permethrin 2EC, cypermethrin 5EC, fenvalerate 5EC, and deltamethrin 2.5EC were obtained locally. Insects Pupae of the DBM were collected from three locations and reared on cabbage in the laboratory. A population from Selo in Central Java was identified as a susceptible (S) strain. Populations from the other two locations, Kopeng in Central Java and Lembang in West Java, were reported to be resistant (R) to the synthetic pyrethroids. Bioassay procedure The standard test for determining LD50 values by topical application of insecticides was used (ESA 1970, and Heinrichs et al 1981). Insecticide in 0.05 µl acetone was applied to the dorsal thoracic surface of 3rd instar larvae. The larvae were then transferred to 9 cm diam petri dishes containing cabbage leaves and maintained in rearing room at 25 C, 70% RH, and at a photoperiod of L:D 12:12. Ten untreated larvae were placed in a petri dish containing cabbage leaves. Each of three replicates had at least 10 larvae per insecticide concentration. A minimum of six concentrations, together with a control, were used for each bioassay. Mortality was recorded after 24 h and analyzed by probit analysis (Finney 1971). Laboratory Study II (1983) This experiment was conducted at Pacet in West Java. Insecticides Permethrin 2EC, cypermethrin 5EC, fenvalerate 5EC, carbaryl 85WP, and Bacillus thuringiensis strain HD 1 were obtained locally.

3 Effect of Insecticides on DBM and Its Parasitoid 315 Insects Third and/or fourth instar larvae of DBM were collected from four locations and reared on cabbage. A population from Tawangmangu in Central Java was identified as a susceptible (S) strain, and populations from Lembang and Pacet in West Java and Kopeng in Central Java were reported to be resistant (R) to the synthetic pyrethroids. Pupae of Diadegma eucerophaga Horstm, one of the most promising biological control agents of DBM, were also collected from Lembang and Pacet and reared separately on DBM larvae. Bioassay procedure Toxicity measurements for synthetic pyrethroids and carbamate insecticides were made by using the procedure of Plapp and Vinson (1977). DBM Twenty 2nd or 3rd instar larvae were exposed to residues of insecticides on the inner surfaces of 9 cm diam petri dishes. These dishes were treated with acetone solutions of each insecticide. Acetone only was used for the control. One hour after the exposure, the larvae were transferred to untreated petri dishes containing cabbage leaves. Diadegma eucerophaga Ten three to five day-old adult females of D. eucerophaga were exposed to residues of insecticides on the inner surfaces of 25 mm od x 20 cm test tubes. These tubes were treated with acetone solutions of each insecticide. Acetone only was used in the control. One hour after exposure, the insects were transferred to untreated test tubes containing a cotton plug soaked in a 10% honey in water solution, and they were maintained in a rearing room. All petri dishes and test tubes were maintained at 25 C, 70% RH and at a photoperiod of L:D 12:12 during the observation period. Mortality determinations were made 48 h after initial exposure. Toxicity measurement for B. thuringiensis was made by the procedure of Busvine (1971). Five week-old cabbage plants were sprayed with water solutions of B. thuringiensis. Water only was used for the control. Twenty 2nd or 3rd instar DBM larvae were confined on the treated plants. Mortality determinations were made 72 h after exposure. LC50 and LC50 and slope values for each insecticide against all field strains were calculated with maximum likelihood probit analysis (Finney 1971). Field Experiment I, West Java (1982) Two field experiments were conducted at Lembang and Segunung. Cabbage cultivar Gloria Osena was used at Lembang and K K Cross at Segunung. Six treatment plots including standard insecticide and control replicated four times were arranged in a randomized complete block design. The cabbage plants were transplanted at 80 x 50 cm apart in 8 x 5 m plots which contained 100 plants. Insecticidal dosage and treatments were as follows: fenvalerate 5EC (0.08 kg AI/ha), permethrin 2EC (0.04 kg Al/ha), cypermethrin 5EC (0.08 kg AI/ha), deltamethrin 2.5EC (0.03 kg AI/ha), and diethquinalphion 25EC (0.5 kg Al/ha) used as a standard check. Sprays were applied with a semiautomatic knapsack sprayer and depending on the age of the crops a spray volume of 500 to 1100 I/ha ( average 800 I/ha) was used. The first application started at 14 days after planting (DAP) and was repeated once every week thereafter when the population reached the economic injury level (action threshold or control threshold). The threshold level at Lembang was 0.1 larvae/plant starting 13 DAP up to 69 DAP (Chalfant et al 1979). At Segunung the threshold level was 0.1 larvae/plant, starting 13 DAP up to 34 DAP (Chalfant et al 1979) and intermediate injury level was P=41-60%, starting

4 316 Iman, Soekarna, Situmorang, Adiputra, and Manti 41 DAP up to 62 DAP (Sastrosiswojo et al 1981). Standard check insecticide was applied at weekly intervals starting at 14 DAP up to 70 DAP at Lembang and 63 DAP at Segunung. Ten plants within each dot were selected systematically. The numbers of DBM and C. binotalis larvae on each plant were recorded at weekly intervals starting 13 and 15 DAP up to 71 DAP of Lembang and 64 DAP at Segunung. Percentage injury level was calculated as follows: P = percentage injury level; n = total number of leaves in an infestation class; v = numerical value of infestation class (0 to 5); where 0 = no leaf damage; 1 = 20% of the total leaf area damaged; 2 = 40% of the total leaf area damaged; 3 = 60% of the total leaf area damaged; 4 = 80% of the total leaf area damaged; and 5 =all of the leaf area damaged, and N = total number of leaves observed. Counting was conducted every week starting 41 DAP up to 69 DAP for Lembang and 43 DAP up to 64 DAP for Segunung. In each plot, 10 3rd or 4th instar larvae of DBM were collected at random and reared in the rearing room to determine the percentage of parasitism by D. eucerophaga. The insects were collected starting 16 DAP up to 65 DAP for Segunung and 37 DAP up to 72 DAP for Lembang. Yields and ability to develop heads were observed at harvest time. Field Experiment II, West Sumatra (1982) The experiment was conducted at Air Anget, Tanah Datar, West Sumatra. The statistical design, plot size, planting distance, insecticidal treatments and so on were similar to those in Field Experiment I. Field Experiment Ill, West Sumatra (1983) The location of the experiment was the same as Field Experiment II. The insecticidal treatments were: B. thuringiensis HP 32 kg AI/ha; B. thuringiensis WP 32 kg AI/ha; fenvalerate 5EC 0.08 kg AI/ha; cypermethrin 5EC 0.08 kg AI/ha; B. thuringiensis HP 16 kg product + fenvalerate 5EC 0.04 kg AI/ha; B. thuringiensis WP 16 kg product + cypermethrin 5EC 0.04 kg Al/ha; B. thuringiensis HP 16 kg product + cypermethrin 5EC 0.04 kg Al/ha; B. thuringiensis WP 16 kg product + fenvalerate 5EC 0.04 kg AI/ha; quinalphos 25EC 0.5 kg AI/ha; and control. The observations and insecticidal applications were conducted in the same way as in Field Experiments 1 and II. Laboratory Study I(1982) Results and Discussion Among the four synthetic pyrethroid insecticides tested against the three field strains of DBM, LD50 values of permethrin for the Kopeng and Lembang strains were 3 and 11 times higher compared to the Selo strain. These data indicated the possibility of development of resistance to permethrin in the Kopeng and Lembang strains. Therefore it appears wise not to use synthetic pyrethroids in Lembang area, though in Kopeng these insecticides can still be used in combination with other control practices.

5 Effect of insecticides on DBM and Its Parasitoid 3 17 Laboratory Study II (1983) This study indicated that most of the field strains of DBM had already developed resistance to all three synthetic pyrethroids (Table 1). Resistance levels to cypermethrin were much lower than those to permethrin and fenvalerate. Tawangmangu strain was more susceptible to permethrin and cypermethrin than the other strains, but it was more resistant to fenvalerate than Pacet strain. This was at least partly due to the fact that the farmers from the Pacet area prefer to use carbamate insecticides rather than synthetic pyrethroids. Table 1. Resistance ratios of DBM strains from four locations to selected insecticides Location Resistance ratios Permethrin Cypermethrin Fenvalerate Carbaryl B. thuringiensis Kopeng Pacet Lembang Tawangmangu Fenvalerate has been used in Kopeng, Lembang and Tawangmangu since 1981, whereas the other compounds were introduced more recently. However, levels of resistance appeared in most field strains. This finding coincided with a general observation that the effectiveness of synthetic pyrethroids in controlling DBM has declined significantly in the field. The LC50 values of fenvalerate for Kopeng and Lembang strains were 10 and 18 times those' of to Pacet strain. The resistance ratio of Kopeng strain has increased 10 fold compared with the 1982 value. Since 1977, the microbial insecticide B. thuringiensis, has been introduced into Lembang (Sudarwohadi and Said 1977). This insecticide is still effective in controlling DBM and there is no indication of development of resistance (Table 1). D. eucerophaga did not show any development of resistance except in the case of Lembang strain to fenvalerate, which exhibited a resistance ratio of 3 compared to Pacet Strain (Table 2). This indicated that fenvalerate has been used intensively in the Lembang area. Data on the selectivity of four insecticides to DBM vs the parasitoid are presented in Table 3. The data show that, in general, synthetic pyrethroids are more toxic to the parasite than to DBM. The results of this study suggest that DBM has become resistant in varying degrees to synthetic pyrethroids. The LC50 values obtained indicate that failure in DBM control is possible if the present insecticide application practices continue. Ten to 15 insecticide Table 2. Toxicity of four insecticides to female adult of Diadegma eucerophaga Table 3. Selectivity of four insecticides against D. eucerophaga Insecticide Strain LC50ª RR Selectivity ratioª Insecticide Permethrin 2EC Pacet Pacet Lembang Lembang Permethrin Cypermethrin 5EC Pacet Cypermethrin Lembang Fenvalerate Fenvalerate 5EC Pacet Carbaryl Carbaryl 85WP Lembang Pacet ªLC50 to DBM/LC50 to parasite. Lembang a LC50 value, based on µg of insecticide per test tube. b RR = resistance ratio.

6 318 Iman, Soekarna, Situmorang, Adiputra, and Manti sprays are not uncommon for DBM control on cabbage in these areas. Most of the applications contain pyrethroid insecticide. Field Experiment I, West Java (1982) At Lembang, even at the first observation, the population of DBM had reached the threshold level of 0.1 larvae/plant except in the cypermethrin plot (13 DAP) and deltamethrin plot (20 DAP). Nine sprays of fenvalerate and diethquinalphion and eight of permethrin, cypermethrin and deltamethrin provided excellent insect control (Table 4). The synthetic pyrethroids were more or as effective as the standard check. All synthetic pyrethroids tested were also effective in controlling the population of C. binotalis. Table 4. Effectiveness of selected insecticides against DBM at Lembang 1982ª Insecticide Number of larvae/plant sample at DAP Fenvalerate 5EC 0.13a 0.08a 2.18a 1.68b 2.40abc 0.92bc 0.30a 0.20a Permethrin 2EC 0.14a 0.00a 2.30a 0.73a 1.25a 0.36a 0.20a 0.08a Cypermethrin 5EC 0.00a 0.00a 3.03a 1.48ab 1.55ab 0.50ab 0.30a 0.13a Deltamethrin 2.5EC 0.10a 0.03a 2.35a 1.00ab 1.47ab 0.37a 0.35a 0.15a Diethquinalphion 25EC 0.08a 0.08a 2.75a 1.78b 2.78bc 1.23c 0.73a 0.28a Control 0.05a 0.30b 6.13b 7.24c 3.52c 3.18d 2.82b 2.99b ªlnsecticide was applied when the larval population reached 0 1 larvae/plant sample Average of 40 plant samples, DAP=days after planting Means in each vertical column followed by the same letter are not significantly different at the 5% level according to Duncan's multiple range test At Segunung, the DBM population was low; and only one spray per week of each of fenvalerate, cypermethrin and deltamethrin was needed up to 36 DAP. Starting at 41 DAP, however, the percent injury level had reached at intermediate stage (above 40%), which necessitated two to three more sprays (Table 5). Synthetic pyrethroids were as effective as the standard check. Table 5. Percentage injury level of the plant samples one day before spraying, Segunung, 1982 Insecticide Percent injury level at DAPª Fenvalerate 5EC 17.19a 44.92b b b Permethrin 2EC 43.75cd bc 43.00b Cypermethrin 5EC 32.03bc 41.80b 40.23bc 49.22b Deltamethrin 2.5EC 46.09cd 39.45b 39.45bc 43.36b Diethquinalphion 25EC 8.20a 9.38a 9.77a 10.16a Control 51.56d b 55.86c 57.03b ªAverage of 40 plant samples; insecticide was applied when percentage injury level had reached at an intermediate stage (41-64 dap): DAP = days after planting. Means in each vertical column followed by the same letter are not significantly different at the 5% level according to Duncan's multiple range test. Percent injury level In general the percent injury levels were significantly lower in insecticide-treated plots compared to the standard check and control plots. However, they were still at an intermediate stage (30-40%). This suggested that the synthetic pyrethroids had intermediate toxicity to Lembang and Segunung strains (Table 6).

7 Effect + Insecticides on DBM and Its Parasitoid 319 Table 6. Percentage injury level of the plant samples one day before spraying Injury level (%) at DAPª Insecticide Lembang Segunung Fenvalerate 5EC 30.84a 42.66ab 45.00a 18.75a b Permethrin 2EC 30.89a 39.65a 39.76a 39.06b 42.19bc Cypermethrin 5EC 31.44a 42.15a 39.82a b 40.23bc Deltamethrin 2.5EC 31.76a 38.23a 43.09a 43.36b 43.36bc Diethquinalphion 25EC 40.82a 51.19ab 56.00b 8.20a 10.16a Control 65.68b 81.54c 84.19c 52.73b 55.86c a Average of 40 plant samples, DAP = days after planting. Means in each vertical column followed by the same letter are not significantly different at the 5% level according to Duncan's multiple range test Laboratory tests had earlier shown that DBM had developed resistance to these synthetic pyrethroids. D. eucerophaga parasitism of DBM larvae in general, insecticide application did not affect the parasitism of DBM by D. eucerophaga, except at 44 DAP in the fenvalerate, permethrin, deltamethrin, and diethquinalphion plots (Table 7). The data also showed that cypermethrin was slightly safer for the parasite than the other synthetic pyrethroids. This finding agrees with those reported by Tonny (1982) and Pardede (1980). Table 7. Parasitism of DBM larvae by D. eucerophaga in insecticide treated plots. Lembang 1982 Insecticides Parasitism (%) at DAPª Fenvalerate 5EC 40a 32bc 25a 23a 26a 29a Permethrin 2EC 45a 22a 22a 30a 33a 15a Cypermethrin 5EC 55a 35cd 22a 37a 19a 33a Deltamethrin 2 5EC 55a 30bc 18a 37a 27a 20a Diethquinalphion 25EC 35a 12a 18a 21 a 27a 31 a Control 67a 45d 30a 35a 43a 49a a DAP = days after planting Means in each vertical column followed by the same letter are not significantly different at te 5% level by Duncan s multiple range test Field Experiment II, West Sumatra (1982) DBM populations From the first observation (8 DAP), the larval population of DBM always exceeded the threshold level of 0.1 larvae/plant in all the experimental plots (Table 8). Therefore, insecticides were applied at weekly intervals. A total of 11 sprays were applied. The first application did not show any effect on DBM (11 DAP). At the subsequent applications, all the insecticides could effectively control the pest. All synthetic pyrethroids were more or as effective as the standard check quinalphos. These results were similar to the results at Lembang and Segunung. Fenvalerate was the most effective in controlling DBM. C. binotalis population was very low throughout the test. Percent injury level All insecticides tested reduced the percent injury levels (Table 8). The synthetic pyrethroids provided excellent DBM control. The percent injury levels were lower compared to the standard check quinalphos at 49 DAP. D. eucerophaga parasitism of DBM larvae In contrast to the Lembang and Segunung experiments, in West Sumatra, only during the first three observations (35, 39 and 43 DAP) did insecticides fail to adversely affect the parasitoids. However,

8 3 20 Iman, Soekarna, Situmorang, Adiputra, and Manti Table 8. Effect of insecticide spray at one day before and three days after spraying on DBM population, injury level, and yield at Air Angat, West Sumatra, 1982ª lnsecticides Number of larva/plant sample at DAP Percent injury level Fenvalerate 0.38a 0.38a 0.15b 0.43b 0.43c 1.05c 0.68c 1.28c 8.61c 36.8a Permethrin 0.28a 0.25a 0.55b 0.88b 0.68c 2.45c 1.80c 3.18c 16.10c 26.1b Cypermethrin 0.48a 0.40a 0.73b 0.48b 0.78c 2.95c 1.83c 2.63c 12.70c 25.7b Deltamethrin 0.45a 0.43a 0.93b 1.05b 2.75bc 6.93b 3.80c 4.93c 16.69c 33.4a Quinalphos 0.45a 0.35a 0.83b 1.28b 3.33b 7.98b 9.78b 12.15b 33.63b 11.3c Control 0.30a 0.35a 1.85a 3.03a 5.58a 12.63a 17.40a 17.80a 50.63a 8.4c a Insecticide was applied when the larval population reached 0.1 larvaelplant sample. See text for insecticide formulation and AI used. C Average of 40 plant samples: DAP = days after planting. d At 40 DAP Means in each vertical column followed by the same letter are not significantly different at the 5% level according to Duncan's multiple range test. Yield t/ha beginning at 47 DAP, the insecticide application did have some adverse affect on the parasitism of DBM larvae (Table 9). Only the standard check, quinalphos, showed no significant difference in the percent parasitism compare to insecticide-free control plots. Head development and yields The numbers of heads developed in the synthetic pyrethroid plots were higher than in the standard check quinalphos and control plots. Consequently the yields in pyrethroid-treated plots were significantly higher than in the standard check and control plots. The highest yield of 36.8 t/ha was obtained in the fenvalerate plot (Table 8). Table 9. Parasitism of DBM larvae by D. eucerophaga in insecticide treated plots at Air Angat, West Sumatra, 1982ª Insecticides Parasitism (%) at DAP Fenvalerate 5EC 17bc 15bc 23ab 25bc 18b 18d 20c Permethrin 2EC 19bc 33abc 13b 18c 30c 25b 60a Cypermethrin 5EC 24bc 38ab 28a 15c 20d 13b 38bc Deltamethrin 2 5EC 10c 15bc 25ab 23bc 13d 25b 33bc Quinalphos 25EC 45a 50a 33a 38a 48a 45a 63a Control 33ab 33abc 35a 30ab 38b 48a 50ab ªObservations were conducted at two days after spraying See text for AI used DAP=days after planting Means in each vertical column followed by the same letter are not significantly different at the 5% level according to Duncan's multiple range test Field Experiment Ill, West Sumatra (1983) Based on the previous laboratory and field experiments, the results suggested that DBM had developed resistance to synthetic pyrethroids and that these chemicals had an adverse affect on the parasitoid of DBM. However, synthetic pyrethroids were still preferred by farmers for controlling DBM. Therefore, in this experiment, we looked for alternative control method by using a microbial insecticide and mixing it with synthetic pyrethroids.. DBM population From the first observation (13 DAP), the larval population of DBM was already above the threshold level of 0.1 larvae/sample plant in all the plots (Table 10). The insecticides were sprayed at weekly intervals, because each individual insecticide spray failed to reduce the larval population to below the threshold level. Microbial

9 Effect of Insecticides on DBM and Its Parasitoid 32 1 Table 10. Effect of insecticide mixtures on DBM larval population at one day before and two days after application, on injury level, and yield of cabbage at Air Angat, West Sumatra. 1983a Insecticideb No. of larvaelplant at DAP Injury Yield % at t/ha DAP Bt HP 5.57ab 1.80b 1.33c 1.30c 4.53cd 2.47b 27.78c 36.78ab Bt WP 3.63b 1.73b 0.57c 0.53c 2.03cd 1.07b 26.15c 37.78ab Fenvalerate 5.10ab 1.90ab 1.70c 0.90c 4.27cd 3.60b bc b Cypermethrin 7.37a 2.13ab 1.80c 1.40c 3.37cd 4.33b 33.21ab 30.46b Bt HP+Fen 3.42b 1.53b 1.13c 1.13c 4.50cd 3.77b 27.46c 37.78ab Bt WP + Cyper 4.23ab 1.80b 1.20c 1.27c 2.30cd 2.00b 26.32c 34.87ab Bt HP + Cyper 4.27ab 1.97ab 1.93bc 1.23c 4.90bc 4.07b 27.09c 37.21ab Bt WP + Fen 6.33ab 1.73b 0.60c 0.80c 1.53d 1.67b 26.95c 42.76a Quinalphos 5.20ab 2.43ab 3.17ab 3.80a 14.87a 10.40a 35.91a 16.30c Control 5.50ab 4.47a 3.43a 2.63b 7.73b 8.83a 34.98a 15.97c a Insecticide was applied when the larval population reached 0.1 larva/plant. b See text for insecticide formulation and AI used. c Average of 40 plants. d Average of 30 plants. DAP = days after planting. e Bt = Bacillus thuringiensis. f Fen = Fenvalerate. g Cyper = Cypermethrin. Means in each vertical column followed by the same letter are not significantly different at the 5% level according to Duncan's multiple range test See text for the formulation and rate of application of the insecticides. insecticides applied alone or as mixtures with fenvalerate or cypermethrin gave a better control than either fenvalerate or cypermethrin alone or the standard check, quinalphos. A mixture of B. thuringiensis WP with fenvalerate or cypermethrin performed better than a mixture of B. thuringiensis HP with fenvalerate or cypermethrin. The synthetic pyrethroids alone were less effective. Percent injury level The microbial insecticide applied alone or as a mixture could reduce the percent injury level of DBM. Of the two synthetic pyrethroids tested, cypermethrin was less effective. Parasitism DBM larvae by D. eucerophaga The parasitism level of DBM in the microbial insecticide-treated plots was similar to the parasitism level in the control plot. In contrast to the second field experiment, the synthetic pyrethroid applied alone or as a mixture did not show adverse effects on the parasitoid (Table 11). Head development and yields The head development in all the insecticidal plots was higher than the control plot. The total number of plants which did not develop Table 11. Parasitism of DBM larvae by D. eucerophaga in insecticide treated plots. Air Angat, West Sumatra. 1983a Insecticides 16 Parasitism (%) at DAP Bt HP 10a Od 25a 13b 12a Ob 27a Bt WP 17a 33abcd 17a 36ab 13a 19ab 17a Fenvalerate 25a 60ab 32a 30ab 20a 10ab 22a Cypermethrin 50a 43abc 26a 38a 17a 23a 30a Bt HP + fenvalerate 29a 31abcd 7a 21ab 21a 3ab 23a Bt WP + cypermethrin 43a 67ab 8a 1 Ob 19a 10ab 17a Bt HP + cypermethrin 22a 54ab 22a 26ab 17a 4ab 35a Bt WP + fenvalerate 19a 17cd 18a 33ab 1 la 9ab 32a Quinalpos 32a 58ab 25a 39a 21a 4ab 23a Control 21 a 71 a 19a 24ab 24a 14ab 37a Observations were conducted at two days after spraying. See text for formulation and AI applied. c DAP = days after planting. Means in each vertical column followed by the same letter are not significantly different at the 5% level according to Duncan's Multiple Range Test. d Bt: Bacillus thuringiensis.

10 322 Iman, Soekarna, Situmorang, Adiputra, and Manti heads in the cypermethrin plot was quite high. However, it was still significantly lower than in the standard check quinalphos plots and in control plots. The yields when microbial insecticide was applied alone or as a mixture with synthetic pyrethroids were better than when pyrethroids were applied alone and in the standard check quinalphos plots (Table 10). The highest yield of t/ha was obtained with a mixture of B. t huringiensis W P with fenvalerat e. The results obtained in these three field experiments indicated that synthetic pyrethroids had intermediate to low toxicity to the various field strains of DBM. These insecticides are toxic to the parasitoid. Mixture with a microbial insecticide gave better control and a less adverse effect on parasitoid. However, our studies show that there can be a wide variation in the toxicity of individual insecticides or their mixtures, to both DBM and to the parasitoid. Therefore, comparative field evaluation of the possible candidate insecticides within the class and their mixtures with microbial insecticides or other kinds of chemicals may be necessary to ascertain their effects on the whole natural enemy complex and to evaluate their relative usefulness in integrated pest management programs. Literature Cited Ankersmit, G. W DDT resistance in Plutella maculipennis (Curt.). Lep. in Java. Bull. Entomol. Res. 44: Busvine, J. R A Critical Review of the Techniques for Testing Insecticides. The Commonwealth Institute of Entomology, London. 345 pp. Chalfant, R. B., W. H. Denton, D. J. Schuster, and R. B. Workman Management of Cabbage Caterpillars in Florida and Georgia by 'using Visual Damage Thresholds. J. Econ. Entomol. 72: ESA Second conference on test methods for resistance in insects of agricultural importance. Standard method for detection of insecticide resistance in Heliothis zea (Boddie) and Heliothis verescens (F.). Bull. Entomol. Soc. Am. 16: Finney, D. J Probit Analysis. 3rd. ed. Cambridge University press. Cambridge. 333 pp. Heinrichs, E. A. S. Chelliah, S. L. Valencia, M. B. Arceo, L. T. Fabellar, G. B. Aquino, and S. Pickin Manual for Testing Insecticides on Rice. International Rice Research Institute, Los Banos, Philippines. 134 pp. Oka, I. N Konsep Pengendalian Hama Penyakit Tanaman. LPPP, Bagian Hamma Penyakit. Prasaran pada Rapat Teknis (In Indonesian), Lembaga Penelitian Hortikultur, 8 Maret pp. Pardede, D. B A study of the effects of ULV/CDA and HV insecticide application method against natural enemies of Plutella xylostella (L.), Pieris brassicae (L.) and Brevocoryne brassicae (L.) on Brussels Sprout. MS Thesis, Univ. of London. 77 pp. Plapp, F. W. Jr. and S. B. Vinson Comparative toxicities of some insecticides to the tobacco budworm and its ichneumond parasite. Environ. Entomol. 6: Sastrosiswojo, S., S. Tatty, and A. H. Sutisna Ambang ekonomi ulat pemakan daun kubis di Lembang (In Indonesian). Lembang Research Institute for Horticultural Crops. (unpublished data). Sitanggang, M. S Ambush. Insektisida pyrethroid sintetik terhadap hama hama tanaman (In Indonesian). Kongres Entomologi I, Jakarta Januari pp. Sudarwohadi, S Hubungan antara waktu tanam kubis dengan dinamika populasi Plutella maculipennis Curt. dan Crocidolomia binotalis Zell. (In Indonesian) Bull. Penel. Hort. 3:3-14.

11 Effect of Insecticides on DBM and Its Parasitoid 323 Sudarwohadi, S Hasil hasil pengujian efikasi fenvalerate terhadap hama utama tanaman hortikultura. (In Indonesian). Paper presented at Fenvalerate symposium. Perhimpunan Entomologi Indonesia. August, 23-24, Jakarta, 1983, 37 pp. Sudarwohadi, S. and A. Said Pengujian efikasi Sumicidin 20EC terhadap larva Plutella xylostella dan Crocidolomia binotalis di laboratorium (In Indonesian) (unpublished data). Lembang Research Institute for Horticultural Crops. Sudarwohadi, S. and K. G. Eveleens Biological control of Plutella xylostella on cabbage in Indonesia by the introduced parasite Diadegma eucerophaga. Bull. Penel. Hort. 5: Tonny, K. M Pengujian selektifitas insektisida terhadap larva Plutella xylostella Linn. dan Diadegma eucerophaga Horsts. pada tanaman kubis di laboratorium (In Indonesian). Skripsi Akpernas. Bandung. 73 pp. Woodford, J. A. T., A. L. H. Dibyantoro, R. E. Suriaatmadja; A. H. Sutisna, H. A. J. Moll, K. Palallo, and L. Suparta The use of agrochemicals on potato, tomato and cabbage crops in West Java. Balittan Lembang and QTA pp. (mimeograph).